1. Field of the Invention
The invention relates to an optical configuration, in particular for bidirectional WDM systems with at least three wavelengths. Such optical configurations typically have at least one Mach-Zehnder interferometer with a first arm, a second arm, and at least one directional coupler with a first arm and a second arm. The invention also relates to a transceiving module for bidirectional optical data transmission having such an optical configuration.
In optical telecommunications engineering, multiplexing data that is to be transmitted via an optical conductor maximizes the transmittable data volume. One possibility in this context involves transmitting information independently and simultaneously via one waveguide using a plurality of wavelengths. In particular, what are termed WDM (Wavelength Division Multiplex) systems are known in which information is transmitted in one fiber in parallel on a plurality of data channels of different wavelength. It is necessary in this case for the signals of various light sources to be combined in one optical conductor at the transmitting end, and for the signals of various wavelengths from the incoming waveguide to be split into individual channels for separate detection at the receiving end. Bidirectional data transmission occurs when signals are transmitted in both directions on an optical fiber. This technique can be implemented by using bidirectional modules.
Bidirectional modules are known for two-wavelengths and three-wavelengths WDM applications. The modules for two-wavelengths WDM applications have either a Mach-Zehnder interferometer, a directional coupler or a dielectric filter for separating two received wavelengths. The modules for three-wavelengths WDM applications generally have a hybrid construction of glass fibers, micromirrors, and dielectric filters in order to separate the three wavelengths.
It is accordingly an object of the invention to provide an optical configuration, in particular for bidirectional WDM systems, and a transceiving module for bidirectional optical data transmission that overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and that make available an optical configuration and a transceiving module for bidirectional optical data transmission that are of a simple construction with a high degree of integration. The optical configuration and the transceiving module are intended, in particular, to permit bidirectional optical data transmission using two received and one emitted wavelength.
With the foregoing and other objects in view, there is provided, in accordance with the invention, an optical configuration includes a Mach-Zehnder interferometer and a directional coupler. The Mach-Zehnder interferometer has a first arm and a second arm. The directional coupler has a first arm and a second arm. The Mach-Zehnder interferometer and the directional coupler are interlocked with one another, with one of the arms of the Mach-Zehnder interferometer simultaneously being one of the arms of the directional coupler.
With the objects of the invention in view, there is also provided a transceiving module for bidirectional optical data transmission, in particular for WDM systems with at least three wavelengths, including two separate detection devices, an input/output optical waveguide, and an optical configuration as described above. A first of the detection devices is for detecting a first of the three wavelengths. A second of the detection devices is for detecting a second the three wavelengths. The transmitting device is for transmitting a signal having a third of the three wavelengths. The input/output optical waveguide is for receiving signals of the first and second wavelengths and emitting signals of the third wavelength. The input of the Mach-Zehnder interferometer is for receiving the signals of the two wavelengths that are to be detected separately from the input/output optical waveguide. The Mach-Zehnder interferometer separates the signals of the two wavelengths and feeds them to the separate detection devices. The directional coupler receives the signals of the third wavelength from the optical transmitter and feeds the signals to the input/output optical waveguide by launching the signals of the third wavelength into the arm of the directional coupler simultaneously being one of the arms of the Mach-Zehnder interferometer and the directional coupler.
In accordance with the objects of the invention, the invention therefore encompasses an optical configuration including a Mach-Zehnder interferometer and a directional coupler. The Mach-Zehnder interferometer and the directional coupler are interlocked with one another in such a way that one arm of the Mach-Zehnder interferometer is simultaneously one of the arms of the directional coupler and vice versa; the arm being shared can be called a xe2x80x9ccommon armxe2x80x9d. In this way, the space requirement for the optical configuration is minimized and the degree of integration is raised. The Mach-Zehnder interferometer and the directional coupler are preferably integrated on one chip in this case.
In accordance with a further object of the invention, an optical configuration could include a plurality of Mach-Zehnder interferometers and a plurality of directional couplers, one Mach-Zehnder interferometer and one directional coupler being interlocked with one another in each case in the way according to the invention. It is thereby possible, for example, for Mach-Zehnder interferometers and directional couplers interlocked according to the invention to be cascaded or combined in another way. The exact construction depends in this case on the optical circuit to be implemented.
One arm of the Mach-Zehnder interferometer preferably has a shorter length than the other arm. In this case, the arm of greater length of the Mach-Zehnder interferometer forms one arm of the directional coupler. In particular, the arm of the directional coupler that is simultaneously an arm of the Mach-Zehnder interferometer runs rectilinearly, and so the directional coupler can be designed simply.
In a development of the invention, a phase shift is mounted on one arm of the Mach-Zehnder interferometer. This permits precise setting of the phase difference between the signals running in the two arms of the Mach-Zehnder interferometer. The phase shift compensates for manufacturing tolerances.
The Mach-Zehnder interferometer is preferably constructed to separate a first and a second wavelength presented at the input of the Mach-Zehnder interferometer and relay the output of the interferometer in separate optical paths. The directional coupler is preferably constructed in such a way that signals of a third wavelength that are present on one arm of the directional coupler are launched completely into the other arm of the directional coupler, which is simultaneously an arm of the Mach-Zehnder interferometer, and run in the process in the opposite direction to the signals of the first and second wavelength in this arm.
In an advantageous embodiment, the Mach-Zehnder interferometer has a 3 dB coupler on the input side that splits the incoming signals equally between the two arms. On the output side, the two arms of the Mach-Zehnder interferometer merge into two separate optical paths to which detection units are connected.
The optical configuration is preferably of optically integrated design. In particular, the optical conductors and optical arms of the Mach-Zehnder interferometer and of the directional coupler are of optically integrated design. However, it is also possible in principle to make use of fiber optic structures.
The transceiving module according to the invention is characterized by an optical configuration. The transceiving module of the invention provides for the following:
a) the signals of at least two wavelengths that are to be detected separately are present at the input of the Mach-Zehnder interferometer,
b) signals of two wavelengths are separated by the Mach-Zehnder interferometer and fed to separate detection devices, and
c) signals of a third wavelength, to be coupled outside the module, of the optical transmitter are present at the directional coupler, and the signals are launched into the common arm with the Mach-Zehnder interferometer and are fed to the input/output waveguide.
In accordance with a further object of the invention, a module with a high degree of integration is provided that can separate at least three wavelengths (two incoming and one outgoing).
In a preferred embodiment, the directional coupler is assigned a further directional coupler of which one arm is connected to the directional coupler and of which the other arm is connected to the optical transmitter. In this case, the following are true:
a) radiation emitted by the optical transmitter is launched into the arm connected to the directional coupler of the further directional coupler, and
b) radiation present in the arm connected to the directional coupler and that is launched by the Mach-Zehnder interferometer is not launched into the arm connected to the optical transmitter of the further directional coupler.
This ensures that interfering radiation launched from the interferometer into the directional coupler is not led to the optical transmitter thereby disturbing it.
The transceiving module according to the invention for bidirectional optical data transmission has an optical configuration, there being present at the input of the Mach-Zehnder interferometer signals of at least two wavelengths to be detected separately. The Mach-Zehnder interferometer separates the two wavelengths and feeds them to separate detection devices. An optical transmitting device provides signals of a third wavelength; the signals of the third wavelength are to be coupled outside the module. An optical transmitting device of the module is disposed at the input of the directional coupler and launches the signals of the third wavelength into the common arm with the Mach-Zehnder interferometer. The signals of the third wavelength are thereby fed to an input/output waveguide.
Other features that are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in an optical configuration, in particular for bidirectional WDM systems, and a transceiving module for bidirectional optical data transmission, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.